Cyanide-Free Copper Preplating Electroplating Solution and Preparation Method Therefor

ABSTRACT

The present invention relates to a cyanide-free copper-preplating electroplating solution, wherein the electroplating solution is prepared from following components in mass percent: 1-60% of complexing agent, 0.5-30% of copper salt and the balance of water, wherein the complexing agent has a general formula M x H y P n O 3n+1 R z , wherein M is any one or more of alkali metal ions and NH4+, R is acyl, the copper salt has a general formula Cu x/2 H y P n O 3n+1 R z , x, n and z are positive integers, y is 0 or a positive integer and x+y+z=n+2. A preparing method comprises: (1) preparing a complexing agent: mixing alkali, carbonate or bicarbonate containing M, phosphoric acid and an acidic salt of monoprotic organic acids or polybasic organic acids containing an R group for reacting according to a molar ratio, then carrying one step polymerization on a reaction solution at 100-800° C. for 0.5-10h to obtain a finished product of the complexing agent; (2) preparing a copper salt: uniformly mixing the complexing agent prepared in step (1) with a bivalent copper compound in a water phase system according to a molar ratio, reacting for 0.5-1.0h at 25-100° C., and centrifuging for separation and drying to obtain the copper salt after the reaction; (3) preparing an electroplating solution: uniformly and proportionally mixing respective components to obtain the electroplating solution.

TECHNICAL FIELD

The present invention relates to an electroplating solution, and in particular, to a cyanide-free copper preplating electroplating solution and a preparing method thereof, belonging to the technical field of copper plating of electrochemistry.

BACKGROUND

A copper-nickel-chrome or copper-nickel-imitation gold or copper-multilayer nickel-chrome plating process is an electroplating combined process that is very widely used. At present, a bottom plating copper layer in these electroplating combined processes is obtained by a cyaniding electroplating process, the copper layer can prevent a replacement reaction, influencing a binding force between the plating and a base material, between a plated workpiece and copper, the plating obtained by a copper preplating electroplating solution containing cyanide is fine and good in binding force, and the electroplating solution is very good in plating uniformity, flatness and stability. However, the cyanide is a highly toxic chemical, its lethal amount for people is only 0.005 g, the cyanide harms the body health of an operator and pollutes the environment, in addition, sewage is hard to dispose, a sewage disposal cost is very high, therefore, in order to protect the environment and reduce public hazards, there is an urgent need to develop a cyanide-free copper preplating electroplating solution.

Currently, the cyanide-free copper preplating electroplating solution adopts the following several electroplating processes: 1. pyrophosphate copper plating: potassium pyrophosphate is taken as a complexing agent and has better complexing capacity, the stability constant of a complex formed by copper ions and pyrophosphate radicals is K₁=6.7, K₂=9.0, the electroplating solution taking the potassium pyrophosphate as the complexing agent is stable in quality, can adopt a wider process range, but has a defect that the electroplating cannot be performed on a steel substrate directly, otherwise replacement occurs on the substrate surface and causes a poor complexing capacity, therefore, the electroplating solution taking the potassium pyrophosphate as the complexing agent has a limited application range; 2. citrate copper plating: citric acid has higher complexing capacity and can generate a very stable substance together with the copper ions in the electroplating solution, the stability constant of a complex formed by the copper ions and the citrate radicals is K₂=19.30, no replacement phenomenon is generated on the surface of the steel substrate if such process is adopted to plate copper, but the process has the defect that the electroplating solution taking the citric acid as the complexing agent is not stable enough in quality, dispersity of the electroplating solution needs to be improved, and the electroplating solution is deteriorated at high temperature; 3. HEDP copper plating: HEDP is an organic phosphonate, has well complexing capacity, and can form relatively stable substances when reacting with many metals, the electroplating solution taking the HEDP as the complexing agent has stable quality and good dispersity, but the HEDP has the defect that it is found in actual production that the electroplating solution has a process current density range, a plating easily generates copper powder, iron impurities in the electroplating solution reduces a deposition rate and results in a poor binding force between the plating and the substrate, therefore, the electroplating solution taking the HEDP as the complexing agent is not widely used.

SUMMARY

An objective of the present invention is to solve the defects of prior art and provide a cyanide-free copper preplating electroplating solution.

Another objective of the present invention is to provide a preparing method of a cyanide-free copper preplating electroplating solution.

A technical solution adopted by the present invention to solve the technical problems is as follows:

A cyanide-free copper preplating electroplating solution is prepared from following components in mass percent: 1-60% of complexing agent, 0.5-30% of copper salt and the balance of water, wherein the complexing agent has a general formula M_(x)H_(y)P_(n)O_(3n+1)R_(z), wherein M is any one or more of alkali metal ions and NH4+, R is acyl, the copper salt has a general formula Cu_(x/2)H_(y)P_(n)O_(3n+1)R_(z), x, n and z are positive integers, y is 0 or a positive integer and x+y+z=n+2.

The structure of the complexing agent in aforesaid components is explained by plural examples as follows:

a: when x=1, y=1 and z=n, the complexing agent has a general formula MHP_(n)O_(3n+1)R_(n) and a structural formula is as shown in formula (1):

b: when x=n, y=0 and z=2, the complexing agent has a general formula M_(n)P_(n)O_(3n+1)R₂ and a structural formula is as shown in formula (2):

c: when x=1, y=n−1 and R=2, the complexing agent has a general formula MH_(n−1)P_(n)O_(3n+1)R₂ and a structural formula is as shown in formula (3):

The cyanide-free copper preplating electroplating solution of the present invention is formed by mixing the complexing agent, copper salt and water, wherein the complexing agent is strong in complexing capacity, a complexing constant for copper ions is up to 10²⁶⁻²⁷ and is far superior than that of the common complexing agents in the prior art, the electroplating solution prepared by the complexing agent is greatly improved in stability, the quality of the electroplating solution is high, when the cyanide-free electroplating solution is used for preplating, no replacement reaction occurs between main salt metal ions in the electroplating solution and a metal base material, and no loose replacement structures are generated, therefore, a binding force between an electroplating layer and the metal base material is strong, a plating surface is smooth, and the quality of the electroplating layer is greatly improved.

Preferably, the electroplating solution is prepared from following components in mass percent: 5-45% of complexing agent, 1-20% of copper salt and the balance of water, wherein the complexing agent has a general formula M_(x)H_(y)P_(n)O_(3n+1)R, wherein M is any one or more of Na⁺, K⁺ and NH4+, R is acyl, the copper salt has a general formula Cu_(x/2)H_(y)P_(n)O_(3n+1)R, x, n are positive integers, y is 0 or a positive integer and x+y=n+1. The proportion of the complexing agent, copper salt and water is reasonable, and the cyanide-free electroplating solution under such proportion condition has the best stability and the best quality.

The composition of the complexing agent in the preferable technical solution is explained by plural examples as follows:

d: when y=0 and x=n+1, the complexing agent has a general formula M_(n+1)P_(n)O_(3n+1)R and a structural formula is as shown in formula (4):

e: when y=1 and x=n, the complexing agent has a general formula M_(n)HP_(n)O_(3n+1)R and a structural formula is as shown in formula (5):

f: when y=n−1 and x=2, the complexing agent has a general formula M₂H_(n−1)P_(n)O_(3n+1)R and a structural formula is as shown in formula (6):

A preparing method of a cyanide-free copper preplating electroplating solution comprises:

(1) preparing a complexing agent: mixing alkali, carbonate or bicarbonate containing M, phosphoric acid and an acidic salt of monoprotic organic acids or polybasic organic acids containing an R group for reacting according to a molar ratio, then carrying one step polymerization on a reaction solution at 100-800° C. for 0.5-10 h to obtain a finished product of the complexing agent; or drying the reaction solution firstly, and then performing polymerization at 100-800° C. for 0.5-10 h to obtain a finished product of the complexing agent;

(2) preparing a copper salt: uniformly mixing the complexing agent prepared in step (1) with a bivalent copper compound in a water phase system according to a molar ratio, reacting for 0.5-1.0 h at 25-100° C., and centrifuging for separation and drying to obtain the copper salt after the reaction;

(3) preparing an electroplating solution: dissolving the complexing agent in step (1) in proper amount of water, then dissolving the copper salt in step (2) in the complexing agent water solution in proportion, supplementing the balance of water and uniformly mixing, and then adjusting a pH value to 8.5-9.5 to obtain the cyanide-free copper preplating electroplating solution.

In the preparing method of a cyanide-free copper preplating electroplating solution of the present invention, the production cost is low, the cost performance of a product is high, the drying manner in step (1) is spray drying or flashing drying, a whole preparing process is environment-friendly, the charging quantity in step (1) and step (2) is accurate, the conversion rate of raw materials is up to 100%, impurities in reacted wastewater are low in content and a sewage disposal cost is low.

Preferably, when M is Na⁺, the complexing agent in step (1) is prepared by: mixing sodium hydroxide, sodium carbonate or sodium bicarbonate, phosphoric acid and an acidic salt of monoprotic organic acids or polybasic organic acids containing an R group for reacting according to a molar ratio, then performing one step polymerization on a reaction solution at 200-400° C. for 0.5-10 h to obtain a finished product of the complexing agent; or drying the reaction solution firstly, and then performing polymerization at 200-400° C. for 0.5-10 h to obtain a finished product of the complexing agent.

Preferably, when M is K⁺, the complexing agent in step (1) is prepared by: mixing potassium hydroxide, potassium carbonate or potassium bicarbonate, phosphoric acid and an acidic salt of monoprotic organic acids or polybasic organic acids containing an R group for reacting according to a molar ratio, then performing one step polymerization on a reaction solution at 250-800° C. for 0.5-10 h to obtain a finished product of the complexing agent; or drying the reaction solution firstly, and then performing polymerization at 250-800° C. for 0.5-10 h to obtain a finished product of the complexing agent.

Preferably, when M is NH4+, the complexing agent in step (1) is prepared by: mixing ammonium hydroxide, ammonium carbonate or ammonium bicarbonate, phosphoric acid and an acidic salt of monoprotic organic acids or polybasic organic acids containing an R group for reacting according to a molar ratio, then performing one step polymerization on a reaction solution under 100-300° C. for 0.5-10 h to obtain a finished product of the complexing agent; or drying the reaction solution firstly, and then performing polymerization under 100-300° C. for 0.5-10 h to obtain a finished product of the complexing agent.

Besides the copper salts listed above, the copper salt in the cyanide-free copper preplating electroplating solution can be directly selected from any one or plural from copper sulfate, copper chloride or basic cupric carbonate, and when such technical solution is adopted, the preparing method of a cyanide-free copper preplating electroplating solution comprises:

(1) preparing a complexing agent: mixing alkali, carbonate or bicarbonate containing M, phosphoric acid and an acidic salt of monoprotic organic acids or polybasic organic acids containing an R group for reacting according to a molar ratio, then carrying one step polymerization on a reaction solution at 100-800° C. for 0.5-10 h to obtain a finished product of the complexing agent; or drying the reaction solution firstly, and then performing polymerization at 100-800° C. for 0.5-10 h to obtain a finished product of the complexing agent;

(2) preparing an electroplating solution: dissolving the complexing agent in step (1) in proper amount of water, then dissolving the copper salt in the complexing agent water solution in proportion, supplementing the balance of water, and then adjusting a pH value to 8.5-9.5 to obtain the cyanide-free copper preplating electroplating solution.

The present invention has the beneficial effects:

(1) The cyanide-free copper preplating electroplating solution of the present invention is formed by mixing the complexing agent, copper salt and water, wherein the complexing agent is strong in complexing capacity, a complexing constant for copper ions is up to 10²⁶⁻²⁷ and is far superior than that of the common complexing agents in the prior art, the electroplating solution prepared by the complexing agent is greatly improved in stability, the quality of the electroplating solution is high, when the cyanide-free electroplating solution is used for preplating, no replacement reaction occurs between main salt metal ions in the electroplating solution and a metal base material, and no loose replacement structures are generated, therefore, a binding force between an electroplating layer and the metal base material is strong, a plating surface is smooth, and the quality of the electroplating layer is greatly improved.

(2) The cyanide-free copper preplating electroplating solution can be used for electroplating at process temperature from normal temperature to 65° C., the deposition rate of a plating is faster, actual production requirements are met and the electroplating production efficiency is improved.

(3) The dispersity of the cyanide-free copper preplating electroplating solution of the present invention at higher process temperature and the binding force with the plating are obviously improved, since the components of the electroplating solution are not easily volatilized, the composition of the electroplating solution is stable, a prepared plating is compact and has smooth surface, and the defect of instable quality of the electroplating solution caused by the fact that components of the electroplating solution in the prior art are easily volatilized at higher temperature is avoided.

(4) The cyanide-free copper preplating electroplating solution of the present invention can be well combined with metal base materials, has no corrosion to the metal base materials, is wide in application range, and especially prevents the corrosion to the metal base materials caused by the electroplating solution in the prior art when applied to multiple metal base materials such as zinc, aluminum, magnesium or alloy thereof.

DESCRIPTION OF EMBODIMENTS

The technical solution of the present invention is further and specifically explained by specific embodiments.

Reagents or raw materials in each embodiment are conventional materials purchased from the market, the purity is analytically pure and the percent in each embodiment is mass percent.

Embodiment 1

A preparing method of a cyanide-free copper preplating electroplating solution comprises the following steps:

(1) preparing a complexing agent, wherein the complexing agent has a general formula M_(x)H_(y)P_(n)O_(3n+1)Rz, wherein x=3, y=0, n=2 and z=1, M is K⁺, R is acetyl and a specific structural formula is as follows in formula (9):

mixing potassium hydroxide with phosphoric acid and acetic acid for reacting according to a molar ratio of 3:2:1, performing spray drying on the reaction solution to obtain partially polymerized intermediate powder, and placing the intermediate powder in a rake type dryer for polymerization reaction at 250° C. for 10 h to obtain a finished product of the complexing agent after the polymerization reaction is finished;

(2) preparing a copper salt: uniformly mixing the complexing agent prepared in step (1) with copper sulfate in a water phase system according to a molar ratio of 2:3, reacting for 1 h at 25° C. and centrifuging for separation and drying to obtain the copper salt after the reaction, wherein a structural formula of the copper salt is as follows:

(3) preparing an electroplating solution: dissolving 1.0% of the complexing agent in step (1) in 50% of water, then adding 0.5% of the copper salt in step (2) in the complexing agent water solution, adding 48.5% of water and uniformly mixing, and then adjusting a pH value to 8.5 to obtain the cyanide-free copper preplating electroplating solution.

Embodiment 2

A preparing method of a cyanide-free copper preplating electroplating solution comprises the following steps:

(1) preparing a complexing agent, wherein the complexing agent has a general formula M_(x)H_(y)P_(n)O_(3n+1)R_(z), wherein x=3, y=0, n=3 and z=2, M is K⁺ and Na⁺, R is acetyl and a specific structural formula is as follows:

mixing sodium hydroxide with phosphoric acid and acetic acid for reacting according to a molar ratio of 3:3:2, performing flashing drying on the reaction solution to obtain partially polymerized intermediate powder, and placing the intermediate powder in a rake type dryer for polymerization reaction at 200° C. for 10 h to obtain a finished product of the complexing agent after the polymerization reaction is finished;

(2) preparing a copper salt: uniformly mixing the complexing agent prepared in step (1) with copper sulfate in a water phase system according to a molar ratio of 2:3, reacting for 0.5 h at 100° C., and centrifuging for separation and drying to obtain the copper salt after the reaction, wherein a structural formula of the copper salt is as follows:

(3) preparing an electroplating solution: dissolving 30.0% of the complexing agent in step (1) in 40% of water, then adding 10% of the copper salt in step (2) in the complexing agent water solution, adding 20.0% of water and uniformly mixing, and then adjusting a pH value to 8.8 to obtain the cyanide-free copper preplating electroplating solution.

Embodiment 3

A preparing method of a cyanide-free copper preplating electroplating solution comprises the following steps:

(1) preparing a complexing agent, wherein the complexing agent has a general formula M_(x)H_(y)P_(n)O_(3n+)1R_(z), wherein x=1, y=100, n=100 and z=1, M is Na⁺, R is acetyl and a specific structural formula is as follows:

mixing sodium bicarbonate with phosphoric acid and acetic acid for reacting according to a molar ratio of 1:100:1, performing flashing drying on the reaction solution to obtain partially polymerized intermediate powder, and placing the intermediate powder in a rake type dryer for polymerization reaction at 300° C. for 2.5 h to obtain a finished product of the complexing agent after the polymerization reaction is finished;

(2) preparing a copper salt: uniformly mixing the complexing agent prepared in step (1) with copper sulfate according to a molar ratio of 2:1, reacting for 1.0 h at 25° C., and centrifuging for separation and drying to obtain the copper salt after the reaction, wherein a structural formula of the copper salt is as follows:

(3) preparing an electroplating solution: dissolving 40.0% of the complexing agent in step (1) in 30% of water, then adding 15% of the copper salt in step (2) in the complexing agent water solution, adding 15.0% of water and uniformly mixing, and then adjusting a pH value to 8.7 to obtain the cyanide-free copper preplating electroplating solution.

Embodiment 4

A preparing method of a cyanide-free copper preplating electroplating solution comprises the following steps:

(1) preparing a complexing agent, wherein the complexing agent has a general formula M_(x)H_(y)P_(n)O_(3n+1)R_(z), wherein x=1, y=100, n=100 and z=1, M is Na⁺, R is acylamino formed by dehydrating alanine and a specific structural formula is as follows:

mixing sodium bicarbonate with phosphoric acid and alanine for reacting according to a molar ratio of 1:100:1, performing flashing drying on the reaction solution to obtain partially polymerized intermediate powder, and placing the intermediate powder in a rake type dryer for polymerization reaction at 300° C. for 2.5 h to obtain a finished product of the complexing agent after the polymerization reaction is finished;

(2) preparing a copper salt: uniformly mixing the complexing agent prepared in step (1) with copper sulfate according to a molar ratio of 2:1, reacting for 1.0 h at 25° C., and centrifuging for separation and drying to obtain the copper salt after the reaction, wherein a structural formula of the copper salt is as follows:

(3) preparing an electroplating solution: dissolving 60.0% of the complexing agent in step (1) in 20% of water, then adding 10% of the copper salt in step (2) in the complexing agent water solution, adding 10.0% of water and uniformly mixing, and then adjusting a pH value to 8.5 to obtain the cyanide-free copper preplating electroplating solution.

Embodiment 5

A preparing method of a cyanide-free copper preplating electroplating solution comprises the following steps:

(1) preparing a complexing agent, wherein the complexing agent has a general formula M_(x)H_(y)P_(n)O_(3n+1)R_(z), wherein x=3, y=0, n=2 and z=1, M is Na⁺, R is methyl formed by dehydrating methyl orthophosphoric acid and a specific structural formula is as follows:

mixing sodium hydroxide with phosphoric acid and methyl orthophosphoric acid for reacting according to a molar ratio of 3:2:1, performing flashing drying on the reaction solution to obtain partially polymerized intermediate powder, and placing the intermediate powder in a rake type dryer for polymerization reaction at 300° C. for 5 h to obtain a finished product of the complexing agent after the polymerization reaction is finished;

(2) preparing a copper salt: uniformly mixing the complexing agent prepared in step (1) with copper sulfate according to a molar ratio of 2:3, reacting for 1.0 h at normal temperature, and centrifuging for separation and drying to obtain the copper salt after the reaction, wherein a structural formula of the copper salt is as follows:

(3) preparing an electroplating solution: dissolving 40.0% of the complexing agent in step (1) in 20% of water, then adding 20% of the copper salt in step (2) in the complexing agent water solution, adding 20.0% of water and uniformly mixing, and then adjusting a pH value to 9.5 to obtain the cyanide-free copper preplating electroplating solution.

In the preparing method of a cyanide-free copper preplating electroplating solution, besides the complexing agents in embodiments 1-5, complexing agents in embodiments 6 and 7 can also be used, the complexing agents prepared in embodiments 6 and 7 react with copper sulfate or copper chloride respectively according to a certain molar ratio to generate a copper salt, which is then uniformly mixed with the complexing agent and water in proportion, and a pH value is adjusted to 8.5-9.5 to obtain the electroplating solution of the present invention.

Embodiment 6

A complexing agent has a general formula M_(x)H_(y)P_(n)O_(3n+1)R_(z), wherein x=5, y=0, n=5 and z=2, M is Na⁺, R is acyl formed by dehydrating acetyl and sodium bitartrate and a specific structural formula is as follows:

A preparing method of the complexing agent comprises: mixing sodium bicarbonate, phosphoric acid, acetic acid and sodium bitartrate for reacting according to a molar ratio of 5:5:1:1, then performing flashing drying on the reaction solution to obtain partially polymerized intermediate powder, and placing the intermediate powder in a rake type dryer for polymerization reaction at 400° C. for 0.5 h to obtain a finished product of the complexing agent after the polymerization reaction is finished.

Embodiment 7

A complexing agent has a general formula M_(x)H_(y)P_(n)O_(3n+1)R_(z), wherein x=10, y=1, n=10 and z=1, M is K⁺ and Na⁺, R is acyl formed by dehydrating sodium bitartrate and a specific structural formula is as follows:

A preparing method of the complexing agent comprises: mixing sodium hydroxide, potassium hydroxide, phosphoric acid and sodium bitartrate for reacting according to a molar ratio of 1:9:10:1, then performing spray drying on the reaction solution to obtain partially polymerized intermediate powder, and placing the intermediate powder in a rake type dryer for polymerization reaction at 800° C. for 0.5 h to obtain a finished product of the complexing agent after the polymerization reaction is finished.

Embodiment 8

A complexing agent has a general formula M_(x)H_(y)P_(n)O_(3n+1)R_(z), wherein x=10, y=1, n=10 and z=1, M is Na⁺, R is acyl formed by dehydrating disodium hydrogen citrate and a specific structural formula is as follows:

A preparing method of the complexing agent comprises: mixing sodium carbonate, phosphoric acid and disodium hydrogen citrate for reacting according to a molar ratio of 5:10:1, then performing flashing drying on the reaction solution to obtain partially polymerized intermediate powder, and placing the intermediate powder in a rake type dryer for polymerization reaction at 400° C. for 0.5 h to obtain a finished product of the complexing agent after the polymerization reaction is finished.

The electroplating solutions prepared in embodiments 1-5 are researched as follows.

1. Hull cell test (267 ml)

1.1 Preliminary test: the electronic solutions prepared in embodiments 1-5 are used for sheet plating under the conditions of 25° C., current 1 A (stable) and air stirring for 5 min, and characteristics of relatively stable cell voltage and semi light spots and fine crystal on a large area of the plated sheet are observed under the conditions of stable current in the sheet plating process.

1.2 Current density ranged determined by the Hull cell test

The electronic solutions prepared in embodiments 1-5 are used for sheet plating through Hull under the conditions of 55° C. and current 1 A for 10 min to determine an optimal current density range, and the sheet for sheet plating is a 0.5*70*100 A3 steel sheet, which is sanded and polished with 600# waterproof abrasive paper. A current density of each spot is calculated by referring to an empirical formula J_(k)=45.1-5.24 LgL). It can be obtained by sheet plating and calculating the current density that a current density range of the electroplating solutions prepared in embodiments 1-5 is between 0.5 A/dm² and 2.5 A/dm².

2. Electroplating solution and electroplating performance test

2.1 Determining of current efficiency: a copper coulombmeter is adopted to measure, the current efficiency of the electroplating solution prepared in embodiment 1 is 93.0%, the current efficiency of the electroplating solution prepared in embodiment 2 is 92.8%, the current efficiency of the electroplating solution prepared in embodiment 3 is 93.1%, the current efficiency of the electroplating solution prepared in embodiment 4 is 93.8%, and the current efficiency of the electroplating solution prepared in embodiment 5 is 93.4%.

2.2 Electroplating solution dispersity determining:

A curved cathode method is used to determine the dispersity of the electroplating solution under the conditions of current 1 A, oil-free air stirring and 55° C. for 30 min, a test material adopts a 0.5*70*100 A3 copper sheet, which is sanded and polished with 600# waterproof abrasive paper.

Through determining, the dispersity of the electroplating solution in embodiment 1 is 93.5%, the dispersity of the electroplating solution in embodiment 2 is 92.5%, the dispersity of the electroplating solution in embodiment 3 is 93.3%, the dispersity of the electroplating solution in embodiment 4 is 93.1%, and the dispersity of the electroplating solution in embodiment 5 is 93.3%.

2.3 Determining of covering capacity

An inner hole method is adopted to measure the covering capacity of the electroplating solution, a copper pipe has a size of 10 mm*100 mm, a through hole and blind hole method is adopted, the electroplating solution is at 55° C., a cathode current density is 0.5 A/dm², and time is 5 min. The iron pipe is sectioned to observe a plating condition in the pipe.

The electroplating solutions in embodiments 1-5 are used as test electroplating solutions, after the test, it is found that through holes and blind holes are plated with a copper layer, which indicates that the covering capacity of the electroplating solutions prepared in embodiments 1-5 is good.

2.4 Binding force test

2.4.1 Bending test: a polished iron sheet (A3) which is 0.5 mm thick is adopted, the electroplating solution is at 55° C., a cathode current density is 2 A/dm², and time is 15 min.

The electroplating solutions in embodiments 1-5 are used as test electroplating solutions, after the test, the plated test sheet is repeatedly bent till breakage, no peeling phenomenon exists at the cracks, proving that the plating and a substrate are basically not separated. 2.4.2 Thermal shock test: a polished iron sheet (A3) which is 0.5 mm thick is adopted, the electroplating solution is at 55° C., a cathode current density is 2 A/dm², and time is 15 min.

The electroplating solutions in embodiments 1-5 are used as test electroplating solutions, after the test, the plated test sheet is placed in an oven till 200° C., is continuously baked for 1 h, and is immediately immersed in 0° C. water for shock chilling, and a result is that the plating has no blistering and peeling phenomena.

2.5 Plating tenacity test: an A3 steel sheet which is 0.1 mm thick is passivated with lead acid, and is directly hung in the electroplating solutions prepared in embodiments 1-5 after cleaning, the plating is peeled after the thickness of the plating is 20 μm and is bent for 180 degrees, the bent part is extruded, and the plating is not broken which indicates that the plating is good in tenacity.

2.6 Plating porosity test: a polished iron sheet (A3) which is 0.5 mm thick is adopted, the electroplating solution is 55° C., a cathode current density is 1 A/dm², time is 20 min, and the porosity test is performed by adopting an experiment method of attaching a potassium ferricyanide solution to filter paper.

Potassium ferricyanide is 10 g/1; sodium chloride is 20 g/1.

A test result shows that the porosity of the plating formed by taking the electroplating solutions in embodiments 1-5 as test objects is smaller than or equal to 1/dm².

2.7 Deposition rate determining: current is set to be 1 A, temperature is 55° C., and time is 30 min; a determining result shows that the deposition rate of the electroplating solution prepared in embodiment 1 is 0.6 μm/min, the deposition rate of the electroplating solution prepared in embodiment 2 is 0.62 μm/min, the deposition rate of the electroplating solution prepared in embodiment 3 is 0.56 μm/min, the deposition rate of the electroplating solution prepared in embodiment 4 is 0.52 μm/min, and the deposition rate of the electroplating solution prepared in embodiment 5 is 0.55 μm/min.

The electroplating solutions prepared in embodiments 1-5 are subjected to a pilot test further, wherein pilot test parameters are as follows:

Process flow: steel workpiece, ultrasonic deoiling, water washing 1, water washing 2, anode electrolysis deoiling, water washing 1, water washing 2, pickling deoiling, water washing 1, water washing 2, hydrochloric acid washing, water washing 1, water washing 2, terminal electrolysis deoiling, water washing 1, water washing 2, acid activating, water washing 1, water washing 2, electroplating solution in embodiments 1-5, recycling, water washing 1, water washing 2, acid activating and copper acidizing.

Ultrasonic deoiling: concentration of deoiling powder is 50±5 g/L, temperature is 70±5° C., current density is 1-5 A/dm² and time is 5 min.

Cathode electrolysis deoiling: concentration of electrolysis deoiling powder is 50±5 g/L, temperature is 70±5° C., current density is 1-5 A/dm² and time is 5-7 min.

Anode electrolysis deoiling: concentration of electrolysis deoiling powder is 50±5 g/L, temperature is 70±5° C., current density is 1-5 A/dm² and time is 3-5 min.

Pickling: concentration of technical hydrochloric acid is 15-20%, time is 8-10 min and temperature is room temperature.

Activating: concentration of technical hydrochloric acid is 5-10%, time is 3-5 min and temperature is room temperature.

The electroplating solution in embodiments 1-5: a baume degree is 32-36, a pH value is 8.5-9.5, temperature is 50-55° C., a current density is 0.5-2.5 A/dm², time is 5 min to several hours, and practice proves that the flatness and brightness are still very good till plating to 100 μm.

Through continuous operation of a 50 L pilot test electroplating production line for 20 months and continuous operation of a 350 L pilot test electroplating production line for 11 months, it is proved that the electroplating solution prepared in embodiments 1-5 has reliability, is stable in performance, and has consumption of 10-50 ml/KAH.

Based on the pilot test, process conditions of the electroplating solution prepared in embodiments 1-5 for industrial production are obtained.

1. Steel workpiece:

Process flow: steel workpiece, ultrasonic deoiling, water washing 1, water washing 2, anode electrolysis deoiling, water washing 1, water washing 2, pickling deoiling, water washing 1, water washing 2, hydrochloric acid washing, water washing 1, water washing 2, terminal electrolysis deoiling, water washing 1, water washing 2, acid activating, water washing 1, water washing 2, presoaking, electroplating solution in embodiments 1-5, recycling, water washing 1, water washing 2, acid activating and copper acidizing.

Process conditions:

Electroplating solution density: 32-36 baume degrees

Temperature: 45-65° C.

pH value: 8.60-9.50

Stirring: air stirring plus cathode moving

Anode: electrolysis copper or anaerobic electrolysis copper

Ratio of a cathode area to an anode area: 1:1.5-2

Current: 0.5-2.5 A/dm²

2. Zinc alloy workpiece:

Process flow: zinc alloy workpiece, hot dipping dewaxing, ultrasonic dewaxing, water washing 1, water washing 2, ultrasonic deoiling, water washing 1, water washing 2, anode electrolysis deoiling, water washing 1, water washing 2, hydrochloric acid activating, water washing 1, water washing 2, presoaking in ultrasonic presoaking solution for 30 s, electroplating solution in embodiments 1-5 (placing in a cell in an electrified state at 25-35° C.), recycling, water washing 1, water washing 2, acid activating and copper acidizing.

Process conditions:

Electroplating solution density: 32-38 baume degrees

Temperature: 25-35° C.

pH value: 8.60-9.50

Stirring: air stirring plus cathode moving

Anode: electrolysis copper or anaerobic electrolysis copper

Ratio of a cathode area to an anode area: 1:1.5-2

Current: 0.5-1.5 A/dm²

Aforesaid embodiments are merely preferably solutions of the present invention instead of limiting the present invention in any form, and other variants and modifications can be realized under the premise of not changing the technical solution recorded in claims. 

1. A cyanide-free copper preplating electroplating solution, wherein the electroplating solution is prepared from following components in mass percent: 1-60% of complexing agent, 0.3-20% of copper salt and the balance of water, wherein the complexing agent has a general formula M_(x)H_(y)P_(n)O_(3n+1)R_(z), wherein M is any one or more of alkali metal ions and NH₄ ⁺, R is acyl, the copper salt has a general formula Cu_(x/2) H_(y)P_(n)O_(3n+1)R_(z), x, n and z are positive integers, y is 0 or a positive integer, and x+y+z=n+2.
 2. A cyanide-free copper preplating electroplating solution, wherein the electroplating solution is prepared from following components in mass percent: 20-45% of complexing agent, 0.5-10% of copper salt and the balance of water, wherein the complexing agent has a general formula M_(x)H_(y)P_(n)O_(3n+1)R, wherein M is any one or more of Na⁺, K⁺ and NH₄ ⁺, R is acyl, the copper salt has a general formula Cu_(x/2)H_(y)P_(n)O_(3n+1)R, x and n are positive integers, y is 0 or a positive integer, and x+y=n+1.
 3. A method of preparing the cyanide-free copper preplating electroplating solution of claim 1, the method comprising: (1) preparing the complexing agent by a method that comprises mixing alkali, carbonate or bicarbonate containing M, phosphoric acid and an acidic salt of monoprotic organic acids or polybasic organic acids containing an R group according to a molar ratio to form a reaction solution, optionally drying the reaction solution, and performing one step polymerization of the reaction solution at 100-800° C. for 0.5-10 hours to obtain the complexing agent; (2) preparing a copper salt by a method that comprises uniformly mixing the complexing agent prepared in step (1) with a bivalent copper compound in a water phase system according to a molar ratio, reacting for 0.5-1 hour at 25-100° C., and separating and drying the copper salt after the reaction; and (3) preparing an electroplating solution by a method that comprises dissolving the complexing agent in step (1) in water, dissolving the copper salt in step (2) in the complexing agent water solution in proportion, supplementing the balance of water to form a solution, uniformly mixing the solution, and adjusting a pH value of the solution to 8.5-9.5 to obtain the cyanide-free copper preplating electroplating solution.
 4. The method of claim 3, wherein M is Na⁺, the complexing agent in step (1) is prepared by a method that comprises mixing sodium hydroxide, sodium carbonate or sodium bicarbonate, phosphoric acid and an acidic salt of monoprotic organic acids or polybasic organic acids containing an R group according to a molar ratio to form a reaction solution, and performing one step polymerization on a reaction solution at 200-400° C. for 0.5-10 hours to obtain the complexing agent.
 5. The method of claim 3, wherein M is K⁺, the complexing agent in step (1) is prepared by a method that comprises mixing potassium hydroxide, potassium carbonate or potassium bicarbonate, phosphoric acid and an acidic salt of monoprotic organic acids or polybasic organic acids containing an R group according to a molar ratio to form a reaction solution, and performing one step polymerization on a reaction solution at 250-800° C. for 0.5-10 hours to obtain the complexing agent.
 6. The method of claim 3, wherein M is NH₄ ⁺, the complexing agent in step (1) is prepared by a method that comprises mixing ammonium hydroxide, ammonium carbonate or ammonium bicarbonate, phosphoric acid and an acidic salt of monoprotic organic acids or polybasic organic acids containing an R group according to a molar ratio to form a reaction solution, and performing one step polymerization on a reaction solution under 100-300° C. for 0.5-10 hours to obtain the complexing agent.
 7. The cyanide-free copper preplating electroplating solution of claim 1, wherein the copper salt is selected from the group consisting of copper sulfate, copper chloride, basic copper carbonate, and a mixture thereof.
 8. A method of preparing the cyanide-free copper preplating electroplating solution of claim 7, the method comprising: (1) preparing the complexing agent by a method that comprises mixing alkali, carbonate or bicarbonate containing M, phosphoric acid and an acidic salt of monoprotic organic acids or polybasic organic acids containing an R group according to a molar ratio to form a reaction solution, optionally drying the reaction solution, and performing one step polymerization of the reaction solution at 100-800° C. for 0.5-10 hours to obtain the complexing agent; and (2) preparing an electroplating solution by a method that comprises dissolving the complexing agent in step (1) in water, dissolving the copper salt in the complexing agent water solution in proportion, supplementing the balance of water to form a solution, and adjusting a pH value of the solution to 8.5-9.5 to obtain the cyanide-free copper preplating electroplating solution.
 9. A method of preparing the cyanide-free copper preplating electroplating solution of claim 2, the method comprising: (1) preparing the complexing agent by a method that comprises mixing alkali, carbonate or bicarbonate containing M, phosphoric acid and an acidic salt of monoprotic organic acids or polybasic organic acids containing an R group according to a molar ratio to form a reaction solution, optionally drying the reaction solution, and performing one step polymerization of the reaction solution at 100-800° C. for 0.5-10 hours to obtain the complexing agent; (2) preparing a copper salt by a method that comprises uniformly mixing the complexing agent prepared in step (1) with a bivalent copper compound in a water phase system according to a molar ratio, reacting for 0.5-1 hour at 25-100° C., and separating and drying the copper salt after the reaction; and (3) preparing an electroplating solution by a method that comprises dissolving the complexing agent in step (1) in water, dissolving the copper salt in step (2) in the complexing agent water solution in proportion, supplementing the balance of water to form a solution, uniformly mixing the solution, and adjusting a pH value of the solution to 8.5-9.5 to obtain the cyanide-free copper preplating electroplating solution.
 10. The method of claim 9, wherein M is Na⁺, the complexing agent in step (1) is prepared by a method that comprises mixing sodium hydroxide, sodium carbonate or sodium bicarbonate, phosphoric acid and an acidic salt of monoprotic organic acids or polybasic organic acids containing an R group according to a molar ratio to form a reaction solution, and performing one step polymerization on a reaction solution at 200-400° C. for 0.5-10 hours to obtain the complexing agent.
 11. The method of claim 9, wherein M is K⁺, the complexing agent in step (1) is prepared by a method that comprises mixing potassium hydroxide, potassium carbonate or potassium bicarbonate, phosphoric acid and an acidic salt of monoprotic organic acids or polybasic organic acids containing an R group according to a molar ratio to form a reaction solution, and performing one step polymerization on a reaction solution at 250-800° C. for 0.5-10 hours to obtain the complexing agent.
 12. The method of claim 9, wherein M is NH₄ ⁺, the complexing agent in step (1) is prepared by a method that comprises mixing ammonium hydroxide, ammonium carbonate or ammonium bicarbonate, phosphoric acid and an acidic salt of monoprotic organic acids or polybasic organic acids containing an R group according to a molar ratio to form a reaction solution, and performing one step polymerization on a reaction solution under 100-300° C. for 0.5-10 hours to obtain the complexing agent.
 13. The cyanide-free copper preplating electroplating solution of claim 2, wherein the copper salt is selected from the group consisting of copper sulfate, copper chloride, basic copper carbonate, and a mixture thereof.
 14. A method of preparing the cyanide-free copper preplating electroplating solution of claim 13, the method comprising: (1) preparing the complexing agent by a method that comprises mixing alkali, carbonate or bicarbonate containing M, phosphoric acid and an acidic salt of monoprotic organic acids or polybasic organic acids containing an R group according to a molar ratio to form a reaction solution, optionally drying the reaction solution, and performing one step polymerization of the reaction solution at 100-800° C. for 0.5-10 hours to obtain the complexing agent; and (2) preparing an electroplating solution by a method that comprises dissolving the complexing agent in step (1) in water, dissolving the copper salt in the complexing agent water solution in proportion, supplementing the balance of water to form a solution, and adjusting a pH value of the solution to 8.5-9.5 to obtain the cyanide-free copper preplating electroplating solution. 